Informational masking of negative masking

Abstract

Negative masking (NM) is a ubiquitous finding in near-"threshold" psychophysics in which the detectability of a near-threshold signal improves when added to a copy of itself, i.e., a pedestal or masker. One interpretation of NM suggests that the pedestal acts as an informative cue, thereby reducing uncertainty and improving performance relative to detection in its absence. The purpose of this study was to test this hypothesis. Intensity discrimination thresholds were measured for 100-ms, 1000-Hz near-threshold tones. In the reference condition, thresholds were measured in quiet (no masker other than the pedestal). In comparison conditions, thresholds were measured in the presence of one of two additional maskers: a notched-noise masker or a random-frequency multitone masker. The additional maskers were intended to cause different amounts of uncertainty and, in turn, to differentially influence NM. The results were generally consistent with an uncertainty-based interpretation of NM: NM was found both in quiet and in notched-noise, yet it was eliminated by the multitone masker. A competing interpretation of NM based on nonlinear transduction does not account for all of the results. Profile analysis may have been a factor in performance and this suggests that NM may be attributable to, or influenced by, multiple mechanisms.

Uncertainty about amplitude eliminates negative masking in a pure-tone amplitude discrimination experiment

“…In a previous study ( Conroy et al , 2020 ), we showed that uncertainty induced by random variations in the frequency content of a (nonpedestal) masker can eliminate negative masking in a pure-tone amplitude discrimination experiment. In this study, we showed that uncertainty induced by random variations in the amplitude of the pedestal can do the same.…”

“…Of greater interest for the purposes of this study, however, was how uncertainty about amplitude affected the shape of the roving-level masking functions in the circathreshold region and the extent to which these functions exhibited the characteristic dipper shape and negative masking often observed in circathreshold masking functions obtained under fixed-level conditions (e.g., Hanna et al , 1986 ; Viemeister and Bacon, 1988 ; Shepherd and Hautus, 2009 ; Shepherd et al , 2013 ; Conroy et al , 2020 ). The findings were clear: no dipper shape/negative masking was found for the roving-level condition.…”

“…Whereas the near-miss shows that, for A > A 0 , A JND monotonically increases with A , for A in the region near A 0 , a distinct, nonmonotonic “dip” in the masking function is apparent: as A increases from some very low level below A 0 , A JND first decreases to a minimum value, where A JND < A 0 , before increasing in turn (e.g., Hanna et al , 1986 ; Viemeister and Bacon, 1988 ; Shepherd and Hautus, 2009 ; Shepherd et al , 2013 ; Conroy et al , 2020 ). This improvement in detection performance under “masked” re.…”

“…Currently, however, there is no consensus regarding which best accounts for the available data. In a recent study ( Conroy et al , 2020 ; hereafter, “the previous study”), we tested the predictions of two competing theories of negative masking, one based on nonlinear transduction in the auditory system (e.g., Hanna et al , 1986 ), the other on “intrinsic uncertainty” (e.g., Tanner, 1961 ), and found evidence in support of the latter. We extend that work here, focusing in particular on whether negative masking is obtained under conditions of high observer uncertainty induced by random variations in the amplitude of the pedestal.…”